3GPP LTE (3rd Generation Partnership Project Long Term Evolution, referred to as ‘LTE’ hereinafter) will now be described as an exemplary wireless communication system to which the present invention is applicable.
FIG. 1 illustrates an E-UMTS (Evolved Universal Mobile Telecommunications System) as a wireless communication system. The E-UMTS is a system evolved from UMTS (Universal Mobile Telecommunications System) and currently standardized in 3GPP. The E-UMTS may be referred to as an LTE (Long Term Evolution) system. For details of the technical specifications of UMTS and E-UMTS, refer, respectively, to Release 7 and Release 8 of “3rd Generation Partnership Project; Technical specification Group Radio Access Network”.
Referring to FIG. 1, the E-UMTS includes a user terminal (UE), an eNode B (eNB), and an access gateway (AG) located at the end of the network (E-UMTS) and connected to an external network. The eNB can simultaneously transmit multiple data streams for a broadcast service, multicast service and/or unicast service.
One or more cells are present per base station. A cell sets one of bandwidths of 1.25 MHz, 2.5 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz for a carrier and provides downlink/uplink transmission service to a plurality of UEs. Different cells may provide different bandwidths. An eNB controls data transmission/reception to/from a plurality of UEs. The eNB transmits downlink scheduling information about downlink data to a UE to inform the UE of a time/frequency region in which the downlink data will be transmitted, coding information, data size, hybrid automatic repeat and request (HARQ) related information, etc. The eNB transmits uplink scheduling information about uplink data to the UE to inform the UE of a time/frequency region that can be used by the UE, coding information, data size, HARQ related information, etc. An interface for user traffic or control traffic transmission may be used between eNBs.
While wireless communication technology has been developed into LTE based on wideband code division multiple access (WCDMA), demands and expectations of users and providers continue to increase. Furthermore, technical evolution is needed for future competitiveness of wireless communication technology since other wireless access technologies are under development. For technical evolution, reduction of cost per bit, service availability increase, flexible use of frequency band, simplified structure, open interface, appropriate power consumption of terminals, etc. are required.